Ink trap

An ink trap is a piece deliberately removed from a letter where two strokes meet at a sharp angle: the inside of a K’s junction, the crotch of an N, the corner where a stem takes a diagonal. Printed small on absorbent paper, ink spreads outward from every edge, and in an acute corner it spreads from both edges at once and meets in the middle, so the joint fills in and the letter reads as a blot. Cutting a notch there gives the spread somewhere to go. At the size the face was drawn for, the notch disappears into the ink and the corner looks normal; the trap did its work by not being visible.

The classic case is Matthew Carter’s Bell Centennial, drawn for American telephone directories printed at six point on newsprint at speed. Its traps are enormous, gouges rather than notches, because the ink gain they had to absorb was enormous. That is the honest way to read any trap: its size is a measurement of a specific printing condition, not a style. The same logic reappears without ink whenever a glyph is rendered small and blurred by hinting, antialiasing or a low pixel density, which is why screen faces sometimes carry traps too.

A trap is therefore an optical size decision, and the tell that it belongs to one size and not another. A display cut of the same family drawn for headlines has no ink to absorb and no reason to spend contrast on a notch, so it drops the traps and sharpens the corners instead. Reading a trap as a family’s house style rather than as one master’s answer to one size is how traps end up enlarged to sixty point, where they stop being invisible corrections and start being ornaments. Several contemporary faces do exactly that on purpose, which is a legitimate thing to draw, but it is a different move from the one the term originally names.

Keep it apart from aperture, the other anatomy word about openings. An aperture is the gap where a stroke does not close, the mouth of a c or an e, and widening one is about keeping two letters from being confused. A trap is a notch cut at a corner that is already closed, and it is about keeping one corner from filling in. A letter can easily need both. The specimen on this page draws its letterforms as vector paths rather than setting them in a face, because none of the faces this site loads carries traps, and simulates the ink gain by thickening every edge, which is what spreading ink actually does.